1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device by way of forming bumps, wiring lines, or the like by plating, and an apparatus therefor.
2. Description of the Related Art
Recently, with the advancement of miniaturization of electronic devices, integration densities of ICs and LSIs have been increased. Furthermore, in mounting of semiconductor elements, an electrode pitch is reduced and the number of I/O terminals is increased. In order to respond to a trend that electronic devices are formed into card-like shapes, e.g., card type calculators and IC cards, a demand has arisen for low-thickness of the electronic devices.
A semiconductor element has aluminum electrodes. In a mounting operation, these aluminum electrodes are connected to external terminals. Wire bonding is well known as a method of connecting them. In wire bonding, very thin Au (Al or Cu) wire having a diameter of 25 to 30 .mu.m are sequentially connected by thermocompression or an ultrasonic technique. In this method, automatic wire bonders have been widely applied to save labor, and hence high reliability and productivity are realized. However, it is difficult to respond to demand of an increase in the number of pins, reduction in pitch, and reduction in thickness of electronic devices mounting semiconductor elements, associated with the increase in integration density of semiconductor elements. That is, a longer time is required for bonding as the number of pins is increased, and the reduction in pitch and the reduction in thickness of the electronic devices are interfered because of the presence of connecting wires.
In contrast to the above method, wireless bonding such as the TAB and flip chip methods, to which a great deal of attention has been paid, can solve the above-described problems. According to this method, since no wire is used, one-step bonding can be performed, and reduction in pitch and reduction in thickness of electronic devices can be realized. In addition, automation of this wireless bonding method is promoted. Thus, it is expected that wireless bonding becomes the mainstream of mounting techniques of semiconductor elements from now on.
Generally, in wireless bonding, metallic projections called bumps are formed on aluminum electrodes of semiconductor elements, and the bumps are directly connected to external electrode terminals (Solid State Technology. Mar. "Film Carrier Assemly Process" (1979) p. 52)x' In a conventional method. the bumps are formed by the following process.
First, a plurality of semiconductor elements are formed on a semiconductor wafer, and a large number of aluminum electrodes are formed on the respective semiconductor elements.
A passivation film such as an SiO.sub.2 or Si.sub.3 N.sub.4 film is formed on the entire surface of the wafer. The passivation film is selectively etched to expose the aluminum electrodes.
An underlying metal film is formed on the entire surface of the wafer (including the residual portion of the passivation film) by deposition or sputtering. Then, a resist film is formed on the underlying metal film by photoengraving such that portions of the underlying metal film corresponding to the exposed portions of the aluminum electrodes are formed into openings.
Subsequently, bumps each having substantially the same thickness as that of the resist film are formed on portions corresponding to the resist film opening portions of the underlying metal layer by electroplating using the underlying metal film as a cathode.
Then, the resist film is removed, and the exposed underlying metal film is removed using the bumps as masks.
The above-described conventional bump forming method, however, has the following drawbacks. In a plating process, if bubbles entrapped in a plating solution are attached to the underlying metal and the resist in the neighborhood of the opening portions of the resist film, the bubbles are not removed even if the plating solution is agitated, and plating is performed while the bubbles are attached to the underlying metal and the resist. As a result, no bump may be formed or bumps having insufficient thicknesses may be formed. Especially, as a bump size is decreased with advances in micropatterning of the semiconductor elements, even a small bubble may serve as a mask in a plating and interferes with formation of bumps. Therefore, attachment of bubbles causes a great decrease in yield of semiconductor elements.
In order to eliminate such drawbacks, a surface-active agent is added to a plating solution to prevent bubbles from being attached to an underlying metal layer etc. Such a surface-active agent, however, degrades characteristics of the plating solution, thus posing another problem.